MEXICO CITY (Reuters) - Mexican archeologists have discovered a maze of stone temples in underground caves, some submerged in water and containing human bones, which ancient Mayans believed was a portal where dead souls entered the underworld.

Archeologists Victoria Rojas (front) and Lara Hindersten (back) work at a siteat the village of Tahtzibichen in Merida, Yucatan Peninsula, April 12, 2008.

Clad in scuba gear and edging through narrow tunnels, researchers discovered the stone ruins of eleven sacred temples and what could be the remains of human sacrifices at the site in the Yucatan Peninsula.

Archeologists say Mayans believed the underground complex of water-filled caves leading into dry chambers -- including an underground road stretching some 330 feet -- was the path to a mythical underworld, known as Xibalba.

According to an ancient Mayan scripture, the Popol Vuh, the route was filled with obstacles, including rivers filled with scorpions, blood and pus and houses shrouded in darkness or swarming with shrieking bats, Guillermo de Anda, one of the lead investigators at the site, said on Thursday.

The souls of the dead followed a mythical dog who could see at night, de Anda said.

Excavations over the past five months in the Yucatan caves revealed stone carvings and pottery left for the dead.

"They believed that this place was the entrance to Xibalba. That is why we have found the offerings there," de Anda said.

The Mayans built soaring pyramids and elaborate palaces in Central America and southern Mexico before mysteriously abandoning their cities around 900 A.D.

Archeologist Guillermo de Anda, one of the lead investigators, works at a sitein the village of Tahtzibichen in Merida, Yucatan Peninsula, April 12, 2008.

They described the torturous journey to Xibalba in the Popul Vuh sacred text, originally written in hieroglyphic script on long scrolls and later transcribed by Spanish conquerors.

"It is very likely this area was protected as a sacred depository for the dead or for the passage of their souls," said de Anda, whose team has found ceramic offerings along with bones in some temples.

Different Mayan groups who inhabited southern Mexico and northern Guatemala and Belize had their own entrances to the underworld which archeologists have discovered at other sites, almost always in cave systems buried deep in the jungle.

In the Yucatan site they have found one 1,900-year-old ceramic vase, but most of the artifacts date back to between 700 and 850 A.D.

"These sacred tunnels and caves were natural temples and annexes to temples on the surface," said de Anda.

According to Maya myth, the souls of the dead had to follow a dog with night vision on a horrific and watery path and endure myriad challenges before they could rest in the afterlife.

In one of the recently found caves, researchers discovered a nearly 300-foot (90-meter) concrete road that ends at a column standing in front of a body of water.

"We have this pattern now of finding temples close to the water—or under the water, in this most recent case," said Guillermo de Anda, lead investigator at the research sites.

"These were probably made as part of a very elaborate ritual," de Anda said. "Everything is related to death, life, and human sacrifice."

Stretching south from southern Mexico, through Guatemala, and into northern Belize, the Maya culture had its heyday from about A.D. 250 to 900, when the civilization mysteriously collapsed.

Myth and Reality

Archaeologists excavating the temples and pyramids in the village of Tahtzibichen, in Mérida, the capital of Yucatán state, said the oldest item they found was a 1,900-year-old vessel. Other uncovered earthenware and sculptures dated to A.D. 750 to 850.

"There are stones, huge columns, and sculptures of priests in the caves," said de Anda, whose team has been working on the Yucatán Peninsula for six months.

"There are also human remains and ceramics," he said.

Researchers said the ancient legend—described in part in the sacred book Popul Vuh—tells of a tortuous journey through oozing blood, bats, and spiders, that souls had to make in order to reach Xibalba, the underworld.

"Caves are natural portals to other realms, which could have inspired the Mayan myth. They are related to darkness, to fright, and to monsters," de Anda said, adding that this does not contradict the theory that the myth inspired the temples.

William Saturno, a Maya expert at Boston University, believes the maze of temples was built after the story.

"I'm sure the myths came first, and the caves reaffirmed the broad time-and-space myths of the Mayans," he said.

Underworld Entrances

Saturno said the discovery of the temples underwater indicates the significant effort the Maya put into creating these portals.

In addition to plunging deep into the forest to reach the cave openings, Maya builders would have had to hold their breath and dive underwater to build some of the shrines and pyramids.

Other Maya underworld entrances have been discovered in jungles and aboveground caves in northern Guatemala Belize.

"They believed in a reality with many layers," Saturno said of the Maya. "The portal between life and where the dead go was important to them."